1. Field of the Invention
The present invention relates to a wireless terminal device and a communication control method that selectively switch between communication systems.
2. Related Art
In recent years, LTE (Long Term Evolution) type communication systems have been introduced as communication systems used by wireless terminal devices such as a mobile telephone device, in addition to Circuit Switched (CS) type communication systems (for example, CDMA).
In addition, a CS Fallback function has been defined in 3GPP TS 23.272. With this function, it is possible to notify in an LTE communication system a communication arrival request from a CDMA communication system (For example, refer to 3GPP TS 23.272 V10.3.1, “Circuit Switched (CS) fallback in Evolved Packet System (EPS); Stage 2” 2011-04).
Furthermore, in a case where voice communication initiation is performed using the CS Fallback function, instruction for handover to the CDMA communication system is transmitted from the LTE communication system to a wireless terminal device in response to a communication initiation request from the wireless terminal device. The wireless terminal device that has received the handover instruction performs normal communication initiation processing after switching the wireless to the CDMA communication system.
In addition, a technique is proposed which, when a voice call is completed after performing handover to an CDMA communication system, performs handover to an LTE communication system again, which is given priority over the CDMA communication system (for example, refer to JP2010-147576A).